Microbial Degradation Of Polychlorinated Biphenvls Enhanced By Surfactant-producing Bacterium

Since their persistence, long distance mobility, bioconcentration and biotoxicity, polychlorinated biphenyls (PCBs) have been listed as a category of the first twelve POPs (Persistent Organic Pollutants), which need to be controlled in precedence. Although lots of works have been done, PCBs still remain in the natural environment, especially in the soil. Microbial remediation technologies of PCBs-contaminated soil play significant roles because they can be operated simply with low cost and less secondary contamination. But how to increase the bioavailability of PCBs has always been one of the research challenges. It has been shown that some surfactants can improve the bioavailability of PCBs in the soil, especially the biosurfactants those are more environmentally friendly. But the biodegradation of biosurfactants makes it need to be constantly added throughout the process. Adding surfcant-producing bacterium to contaminated soil for sustainable production can make remediation more convenient and more economical. However, there have been few researches focused on the bioremediation of the organic contaminated soil by surfactant-producing bacterium directly.In this study, the different effects of soya bean lecithin, tea saponin, rhamnolipid, alkyl glycoside, sucrose esterto and P-cyclodextrin on the biodegradation of PCBs in soil were tested. The synergic biodegradation of PCBs by Pseudomonas aeruginosa AB93066 and Rhodococcus ruber SS1 was sudied with traditional methods. The mechanism of synergic biodegradation was explained from the growth of Pseudomonas aeruginosa AB93066, the concentration of the produced rhamnolipid and the degradation of PCBs by Rhodococcus ruber SS1. Then how to apply the synergic effects of Pseudomonas aeruginosa AB93066 and Rhodococcus ruber SS1 on hydrophobic organic-contaminated soil was discussed. The main results of this research are as follows:1) By comparing the influence of several common biosurfactants on the degradation rate of PCBs in the contaminated soil, tea rhamnolipid, saponin, alkyl glycoside, sucrose esterto and P-cyclodextrin were found to increase the degradation rate of total PCBs by approximately 40%,39%,22%,43% and 42% respectively after 30 days. Besides, more low-chlorinated PCBs were degraded with alkyl glycoside, sucrose esterto and β-cyclodextrin added when compared with high-chlorinated PCBs.2) Pseudomonas aenuginosa AB93066 promoted the degradation rates of PCB8, PCB28 and PCB52 by 35.0%,5.1% and 9.6% respectively after mixed cultivation with Rhodococcus ruber SS1. It was also proved that Pseudomonas aeruginosa AB93066 can reduce the lag phases of PCB28 and PCB52. The addition of low-chlorinated PCBs gave Pseudomonas aeruginosa AB93066 longer adjustment phase and logarithmic phase, with shorter stable phase. When it came to decline phase, there were more microbial biomass and rhamnolipid detected than the blank system (without PCBs), which indicates that low-chlorinated PCBs stimulated Pseudomonas aeruginosa AB93066 instead of stressing.3) Enhanced biodegradation of both trichlorodiphenyl and tetrachlorobiphenyl was revealed when comparing the influence of rhamnolipid and Pseudomonas aeruginosa AB93066 on Rhodococcus ruber SS1 and indigenous flora. Decreases of pentachlorodiphenyl were observed in slurry with the presence of rhamnolipid. Neither rhamnolipid nor Pseudomonas aeruginosa AB93066 has influence on the degradation rate of hexachlorodiphenyl or heptachlorodiphenyl.In conclusion, the influence of surfactant-producing bacterium on the biodegradation of PCBs was studied, which showed that surfactant-producing bacterium promoted the biodegradation rate of hydrophobic organic compound in soil. The results will help us to understand the PCBs-biodegradation mechanisms and also provide a new way of the remendiation of PCBs soil contamination.